Publication “Athermal InP-Based 90°-Hybrid Rx OEICs with pin-PDs >60 Ghz for Coherent DP-QPSK Photoreceivers” (R. Kunkel, H.-G. Bach, D. Hoffmann, G. G. Mekonnen, R. Zhang, D. Schmidt and M. Schell, IPRM 2010, 22nd International Conference on Indium Phosphide and Related Materials, May 31-Jun. 4, 2010, Takamatsu Symbol Tower, Kagawa, Japan) discloses an optical device having a 90° optical hybrid unit, photodetectors, and transimpedance amplifiers.